Method and means for neutralizing capacity coupling in audions



April 14, 1925. 1,533,858

L. A. .HAZELTINE METHOD AND MEANS FOR NEUTRALIZING CAPACITY COUPLING INAUDIONS Origifial Filed Dec. 28, 1920 2 Sheets-Sheet 1 QJSWM WLATTORNEYS April 14, 1925'. 1,533,858

' L. A. HAZELTINE mmrnon AND MEANS FORNEUTRAL'IZING CAPACITY coumue INAUDIONS Original Filed Dec. 28, 1920 2 Sheets-Sheet a,

RAmo F REGUENCY OUTPUT RADIO sasauancv INPUT A Q NINVENTOR BY y W! @M awATTORN Patented Apr. 14, 1925.

UNITED STATES PATENT OFFICE.

LOUIS A. HAZELTINE, OF HOBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR--PORATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE.

METHOD AND MEANS FOR NEUTRALIZING CAPACITY COUPLING IN AUDIONS.

Original application filed December 28, 1920, Serial No. 433,729, PatentNo. 1,489,228, dated April 1, 1924. Divided and this application filedDecember 28, 1923. Serial No. 683,249.

To all whom it may concern:

Be it known that I, Lotus A. HAZELTINE, a citizen of the United States,residing at Hoboken, in the county of Hudson, State of New Jersey, haveinvented certain new and useful Improvements in Methods and Means forNeutralizing Capacity Coupling in Audions; and I do hereby declare thefollowing to be a full, clear, and exact description of the invention,such as will en able others skilled in the art to which it app'ertainsto make and use the same.

This invention relates to the neutralization of capacity couplingbetween the grid and plate circuits of an audion, which capacitycoupling results in undesirable reactions of the plate circuit on thegrid circuit. The term audion as used in this application, which is adivision of copending application SerialNo. 433,729, filed December 28,1920, Pat. #1,489,228 issued April 1, 1924, refers to any electricalamplifying device containing an input electrode, re-

ferred to as the grid; an output electrode,

referred to as the plate; and a common electrode, referred to as thefilament; the electric power output being controlled elec- Ytrostatically by the input voltage between the grid and filament.

Capacity coupling between the grid and plate circuits of an audion mayresult in the production of oscillations. In somecases such oscillationsare desired, but in other cases, particularly in amplifiers, suchoscillations are very undesirable, as they may completely mask thesignals which it is desired to amplify.

Again, capacity coupling causes the effective input capacity and theinput conductance of the audion to vary with the impedance in the platecircuit and frequently to reach undesirably high values. A high value ofinput conductance results in loss and thence in weakening of the signalto be amplified. A high value of input capacity may require a lowerinductance in the coil connected to the grid circuit and thus result inlower voltage being impressed on the grid. Capacity coupling thereforeresults in a dimunition of the amplification obtainable from an audionamplifier; and no method has heretofore been devised for eliminatingthis effect.

This invention is directed to the elimination of undesirable effects ofcapacity coupling between the grid and plate circuits of an audion suchas described above. This is accomplished bya special application of thegeneral method disclosed in my United States Letters Patent No.1,450,080, issued March 27, 1923, of which this is a continuation inpart. An auxiliary circuit is provided which is electromagneticallycoupled to one of the two original audion circuits,

which we will call the first circuit, and ca.

pacitively coupled to the other or second circuit. If disturbing voltagethen exists in the second circuit, it will cause currents to flow bothin the first circuit and in the auxiliary circuit, due to the capacitycoup lings. The electromagnetic coupling between the auxiliary circuitand the first. circuit is then arranged so that the magnetic effects ofthese two circuits will neutralize each other and so will result in novoltage across the first circuit. Conversely, if a disturbing voltageexists in the first circuit, it will result in noyvoltage across thesecond circuit by the well-known reciprocal properties of electriccircuits.

The arrangement of the auxiliary circuit will depend on the forms of theaudion circuits. In some cases it is necessary to addcoils or capacitiesto the original audion circuits to provide the required couplin s, whilein other cases the couplings may e obtained from coils present for otherpurposes, and the capacities may be obtained from inherent capacities.

The principle and application of this invention are illustrated in theaccompanying drawings, in which-- Fig. 1 is a circuit diagram showing anaudion circuit with. capacity coupling between the grid and .platecircuits and an arrangement for neutralizing this capacity coupling;

Fig. 2 shows an alternative arrangement for neutralizing such capacitycoupling;

Fig. 3 shows a portion of a multistage audion amplifier withthearrangement of Fig. 1 -for neutralizing undesirable capacity coupling;

Fig. 4 shows a simplification of Fig. 3 by which one winding serves twopurposes;

Fig. 5 shows a radio-frequency oscillator and power amplifier with thearrangement of Fig. l for neutralizing undesirable capacity coupling;

Fig. 6 shows a radio-frequency amplifier with the arrangement of Fig. 2for neutralizing undesirable capacity coupling;

Fig. 7 shows a portion of a multistage audion amplifier with thearrangement of Fig. 2 for neutralizing undesirable capacity coupling;and

Fig. 8 shows a simplification of Fig. 7 by which one winding serves twopurposes.

Referring to Fig. 1, reference character L indicates a coil in the gridcircuit of an audion, Z is an impedance in the plate circuit, and C theinherent coupling capacity between the grid and plate, part of which iswithin the audion and part between the leads to the grid and plate. Toneutralize this capacity coupling, the auxiliary coil L is closelycoupled electromagnetically to the grid coil L and is connected betweenthe filament and the neutralizing capacity C whose other terminal isconnected to the platel (By f closely coupled in this discussion andthose that follow is meant coupled with a coeflicient of couplingsubstantially equal to unity.) If the plate potential varies, a currentwill flow through 0 L and a second current through C and L If thecapacity C is so chosen relatively to the number of turns N and N ofcoils L and L respectively, that O then 2 1 the magnetomotive force of Lwill equal that of L and will cancel it, provided that the coils havethe proper relative polarity-1 viz: the terminals connected togetherbeing of unlike polarity. No voltage will then be induced in either coiland therefore no Variation will occur in the grid potential due to isequal to the variation in the plate potential, assuming the resistancesof the coils negligible in comparison with their reactances. Hence theeffects of capacity coupling will have been eliminated.

Fig. 2 differs from Fig. 1 in that the auxiliary coil L is coupled witha coil L now in the plate circuit instead of "the grid circuit; theneutralizing capacity C is now connected to the grid instead of theplate; and the impedance Z is in the grid circuit instead of in theplate circuit. If in this figure the plate potential varies, a voltagewill be induced in L by the current in L Currents will then flow through0 and also through 0 If the capacity ratio 4 2 of L and L equal to theratio of turns respectively, then the currents through C,

and C will be equal, and no current will tend to flow between the gridand the filament. Hence the effects of capacity coupling will have beeneliminated.

The principle and effectiveness of the above arrangements will in no waybe al tered if an impedance of any character is connected in parallelwith L or L or with L and L combined. This possibility is a consequenceof the substantial unity coupling between L and L Further, the upperterminal of L may terminate at any point in the filament system in Figs.1 and 2, that is, at'any point having substantially the same alternatingcurrent potential as the filament, thus including either filamentterminal or the positive terminal of the plate-circuit battery, sincethe batteries serve simply as conductors for variations in current.

In most applications of this invention it is 2 1 differing from unity.For example, as illustrated in Figs. at and 8, L and L may be the coilsof an amplifier transformer which commonly is arranged to step up thevoltage. Again the coupling capacity C, is usually minute, and it mightbe inconvenient to provide an equal neutralizing capacity C since thiswould be greatly affected in value by the length of connecting wires andby the proximity of other conductors and might be difiicult to adjust.In this case L would be given relatively few turns and G acorrespondingly higher value.

Fig. 3 represents one stage and a portion of the succeeding stage of amultistage audion amplifier. The one stage shown com- ,plely comprisesan audion 1 whose grid 2 is connected to the high-potential terminal 3of the secondary coil L of the input transformer 4 and whose plate 5 isconnected to the high-potential terminal 6 of the primary coil of theoutput transformer 7, which is the input transformer of the succeedingstage. The audio-n and the input transformer of each-stage are enclosedin a compartment having for its walls a conducting screen as 891011. Thelow-potential transformer leads 12 and 13and the filament leads 14 and15 pass out through holes in this screen and are suitably connected tothe batteries, which may be connnon to all stages; while the lead 5-6from the plate of one stage to the transformer primary of the succeediugstage passes through a hole in the screen 9-10 separating these stages.By thisarrangement of the screening compartments the only possiblecapacity coupling between stages lies in the inherent capacity couplingC between the plate 5 with its leads and the grid 2 with its connectedor coupled apparatus. This capacity coupling is neutralized, accordingto the principle of Fig. 1, by connecting in series between the plate 5and the filament lead 1 an auxiliary coil L and a condenser 0 theauxiliary coil L being closely coupled electromagnetically withthetransformer coil L as by the low-potential lead of L connected tofilament lead 14: is of opposite polarity to the low-potential lead 13of L Complete neutralization of capacity coupling will be attained, asin Fig. 1, when the number of turns N of the auxiliary coil L and thevalue of the neutralizing capacity (3 are so chosen relative to thenumber of turns N of L, and to inherent capacity coupling 0 that =F.cdpacity G as small as possible, the leads from the plate 5 to theterminal 6 and to C,

In order to make the coupling should be short and preferably screened byenclosing them in a metal tube 16 electrically connected to the screen891011.

Fig. 4 diflers from Fig. 3 in that coil L here serves both as thetransformer primary coil and as the auxiliary coil for neutralizingcapacity coupling. Like reference characters refer to like partsthroughout. The two transformer coils are closely coupled as by windingthem around the same I iron cores; and their low potential leads 12 and13 are-of opposite polarity. Complete neutralization of capacitycoupling will then be attained, as in Figs. 1 and 2, when the value ofthe neutralizing capacity C, is chosen relative to the number of turns Nand N of coils L and L respectively and to the inherentcoupling capacityC that In Fig. 5. reference character 17 indicates a masterradio-frequency oscillator which impresses a radio-frequency voltage onthe grid of power amplifier 18 through the coil L The amplifiedoscillation is transferred to the antenna circuit 19 through thetransformer 20. The directcurreiit of the grid circuit flows thrbugh theresistance 22, the drop in which causes the grid to have .a suitablenegative bias. Condensers 23 and 24 serve as low-impedanceradio-frequency shunts. This particular form of circuit is but one of avery large number which are suitable for generating oscillations, to anyone of which this invention may be applied without. essential change. Inany case the arrangen'ient for neutralizing the capacity coupling due tothe inherent capacity C, between the plate and the grid, following theprinciple of Fig. 1, consists in connecting an.

. auxiliary coil L and a. neutralizing capacity C in series between the.plate and the filament. Coil L is closely coupled to L and terminals ofunlike polarity are connected together. Complete neutralization ofcapacity coupling will be attained, as in Fig. 1, when the number ofturns N of the auxiliary coil L and the value of the neutralizingcapacity C are so chosen relative to the number of turns N of L 'and tothe inherent coupling capacity 0 that The alternative arrangement ofFig. 2 may be applied to the neutralization of the capacity coupling ina radio-frequency power amplifier as illustrated in Fig. 6.

Fig. 7 shows a. portion of a multistage amplifier and follows the planofFig. 3 except only that the alternative arrangement of Fig. 2 isemployed instead of that of Fig. 1. Fig. 8 is derived from Fig. 7 in thesame way as Fig. 4 is derived from Fig. 3, that is, by employing for theauxiliary coil L thetransformer coil which is notassociated with thecouplingxcapacity C The relative polaritiesand ratio of turns of coils Land L in Figs. 7 and 8 are selected by the same rules as given forthepreceding figures. v I I claim: A

1'. The method of neutralizing capacity coupling between the grid andplate circuits of an audion having a transformer in the plate circuitwhich consists in capacitively coupling the grid ofsaid'audion and asecondary of saidtransformer to cause equal capacity currents to flow toand from the grid whereby such current is prevented from flowing betweenthe grid and the filament system.

2. An electric circuit arrangement for neutralizing capacity couplingbetween the grid and plate circuits of an audion having ,a transformerin the plate circuit thereof, comprising means for capacitively couplingthe grid of said audion and a secondary of said transformer wherebyequal capacity currents due to a. variation in the potential of theplate of said audion are caused to flow to and from the grid thuspreventing suchcurrent from flowing between the grid and filamentsystem.

3. An electric circuit arrangement for neutralizing capacity couplingbetween the grid and plate circuits of an audion due to the capacitybetween the grid and plate electrodes, comprising a coil connected between the platoand the filament system, and an auxiliary coil and aneutralizing capacity connected in series between the grid and thefilament system, said auxiliary coil being closely coupledelectromagnetically to the first coil and having a ratio of turnsthereto equal to the ratio of the coupling capacity to the neutralizingcapacity.

, 4. An electric circuit arrangement for neutralizing capacityLcouplingbetween the grid and plate circuits of an audion due to the capacitybetween the grid and plate,

electrodes, comprising a coil connected between the plate and thefilament system, and

an auxiliary coil and a neutralizing capacity connected in seriesbetween the grid and the filament system, said auxiliary coil beingclosely coupled electromagnetically to the first coil, and having aratio of turns thereto equal to the ratio of the coupling capacity tothe neutralizing capacity, said ratio differing from unity.

5. An electric circuit arrangement for neutralizing capacity couplingbetween the grid andplate circuits of an audion due to the capacitybetween the grid and plate electrodes, comprising a coil connectedbetween the plate and the filament system, and an auxiliary coil and aneutralizing capacity connected in series between the grid and thefilament system, said coils and said neutralizing capacity being soproportioned that variations in plate potential cause equal currents toflow through the coupling capacity and through the neutralizing capacityand prevent such current from flowing betweenthe grid and the filamentsys-' tom.

6. In an electric circuit including an audion, the combination of aconducting screen electrostatically isolating the plate circuit from thegrid circuit except for the grid proper and the leads thereto, a coil inthe plate circuit, and an auxiliary coil and a neutralizing capacityconnected in series between the grid and filament system, saidauxiliarycoil being closely coupled electro magnetically to the first coil and,having a ratio of turns thereto equal to the ratio of the couplingcapacity to the neutralizing capacity.

7. In an electric circuit including an audion, the combination of aconducting screen electrostatically isolating the plate circuit from thegrid circuit except for the grid proper and the leads thereto, a coil inthe plate circuit, and an auxiliary coil and a neutralizing capacityconnected in series between the grid and filament system, said auxiliarycoil being closely coupled electromagnetically to the first coil andhaving a ratio ofturns thereto equal to the ratio of the couplingcapacity to the neutralizing capacity, said ratio differing from unity.

8. In a multistage amplifier including an output transformer and anaudion in each stage, the combination of a conducting screenelectrostatically isolating all stages from each other except for thelead from the grid of each audion to the output transformer of thepreceding stage, a coil eleclromagi'ielically coupled to the primary. ofsaid transformer in each stage, and a capacity in each stage, said coiland said capacity in each stage being connected in series between thegrid and the filament sys tem of the audion in that stage, said filamentsystem comprising all points having substantially the same alternatingcurrent potential as the filament.

9. In a multistage amplifier including in each stage an audion and anoutput transformer having a coil electromagnetically 10. In a multistageamplifier including an" output transformer and an audion in each stage,the combination of a conducting screen electrostatically isolating allstages from each other except for the lead from the grid of each stageto the output transformer of the preceding stage, and a capacityconnected between the grid of the audion in each stage and the secondaryof said output transformer of that stage.

11. In a multistage amplifier including an audion in each stage, thecombination of a transformer coupling audions in adjacent stages, oneterminal of said transformer being connected to a grid electrode and aterminal of the other winding thereof being connected to a plateelectrode of an adjacent audion, said terminals being of oppositepolarity, and a capacity connecting the grid electrodes of the adjacentaudions.

12. In a multistage amplifier including a output transformer having aprimary,and an audion in each stage, means for neutralizing the capacitycoupling between the grid circuit and the plate circuit of each audion,comprising a capacity connected between the grid ofthe audion in eachstage and a coil coupled to the primary of said output transformer ofthat stage.

13. In a multistage audion amplifier including an audion in each stage,means for neutralizing the capacity coupling between the grid and theplate circuit of each audion comprising a ca acity connected between thegrid of each an ion and a point in the plate circuit of said audion ofopposite alternating current polarity to that of the plate.

14'. In a multistage amplifier including an audion in each stage atransformer coupling the audions of adjacent stages and having suchpolarity that the primary terminal connected to the plate of one audionis of opposite polarity to the secondary terminal connected to the gridof the succeeding audion, and a capacity connecting the grid electrodesof the audions in adjacent stages.

"15. In a multistage amplifier including an audion in each stage, meansfor neutralizing the capacity coupling between the grid circuit and theplate circuit of each audion comprising a transformer coup-ling audionsin adjacent stages, one terminal of said transformer being connected toa grid electrode and'a terminal of the'other winding thereof beingconnected to a plate electrode of an adjacent audion, said terminalsbeing of opposite polarity and a capacity connecting the grid electrodeof the audion Whose plate is connected to the second winding of saidtransformer, and a point of the first winding of said transformer.

16. In a multistage amplifier including an audion in each stage meansfor neutralizing the capacity coupling between the grid circuit and theplate circuit of each audion comprising a transformer coupling audionsin adjacent stages, one terminal of said transformer being connected toa grid electrode and a terminal of the other winding thereof beingconnected to'a plate electrode of an adjacent audion, said terminalsbeing of opposite polarity, and a capacity connecting the grid electrodeof the audion whose plate is connected to the second winding of saidtransformer with a point of the first winding of said transformer. V

17. A multistage audion amplifier comprising an audion in each stage,means for neutralizing the capacity coupling between the grid and platecircuits of each audion and means for preventing at all frequenciessubstantial coupling between any two stages thereof except for theconductive coupling on which the amplifying action of the audion.depends.

In testimony whereof I affix my signature.

LOUIS A. HAZELTINE.

